The present invention relates to noise suppression devices and more particularly pertains to actively suppressing vibrational noise produced by a drilling medical instrument in a head of a patient with an intracranial noise suppression apparatus.
In a variety of situations, the effect of environmental noise on people ranges from mere annoyance to severe physiological damage. Consequently, control of noise is very important, especially in the workplace, where its adverse consequences can have a great economic impact. Past efforts at noise control have focused on using sound absorbing materials to mitigate the noise or reducing the amount of exteriorly created noise at its source. However, these conventional noise reduction techniques have minimal effect in reducing stress-inducing vibrational noises on a patient produced by a dentist""s drill and associated ultrasonic cleaning tools.
Unfortunately, high frequency sounds from drilling and ultrasonic cleaning propagate very effectively through a patient""s skull to reach the ear. Consequently, one of the chief complaints received by dentists from their patients is discomfort from noise caused by drilling-type operations in their mouths. Furthermore, the discomfort caused by a drilling noise has been exacerbated due to further increases in the speed of new drilling devices.
Although some noise reduction can be accomplished by muffling a patient""s ears or by using active speaker systems to cancel noise that propagates to the patient""s ears, these efforts have been largely unsuccessful in lessening a patient""s pain, chiefly because they have a negligible effect in reducing the discomfort due to drilling noise as it arrives at the inner ear from propagation paths through the patient""s head. For instance, drilling noise induced particularly in the tooth and the jaw by a drill enters the bone and propagates through the skull and its interior to the temporal bone, and finally to the ear. Many dentists have attempted to mask this drilling noise by providing loud music of the patient""s choice through headphones. However, this method has been rather ineffective at masking the more intense, bone-conducted high-frequency noise that is most objectionable. Furthermore, the loud music interferes with communication between the dentist and the patient.
Additional attempts have been made to reduce the discomfort of a patient by suppressing vibrations propagating through the bone structure and intracranial tissue of the head due to a drilling medical instrument by using active vibration cancellation. For example, U.S. Pat. No. 5,570,426 to Gardner discloses a method and apparatus for active cancellation of vibrational noise produced by a medical instrument in the head of a patient. Vibrations from the instrument, as well as vibrations in the bone structure of the head of the patient, are sensed and processed to generate canceling noise waves that are then fed into the inner ear through headphones or the like. An equalizer shapes the magnitude and phase spectrum of the vibrational noise signal picked up from the drill and delivers an equalized inverse signal to the patient. An automatic adaptive controller adjusts the output from the equalizer using control signals consisting of vibrations from the bone structure and the drill.
Furthermore, U.S. Pat. No. 5,692,056 to Gardner discloses another apparatus for suppression of vibrational noise produced by a medical instrument in the head of a patient. This apparatus employs head-worn vibrators to cancel drill induced vibration at the inner ear. Referring to FIG. 1, the system of U.S. Pat. No. 5,692,056 includes an equalizer 10 that is electrically connected to a drill vibration pickup 12, such as a conventional accelerometer or the like vibration sensor, which in turn is mechanically coupled to a drill 14. Equalizer 10, the input of which is connected to drill vibration pickup 12 through interconnection 16, shapes the magnitude and phase spectrum of the vibration signal picked up from the drill 14 and delivers equalized output signals to a right head-worn vibrator 18a and a left head-worn vibrator 18b, to which it is electrically connected through interconnections 20a and 20b, respectively. The system also includes an adaptive controller 22 that has an input electrically connected to a drill vibrational pickup 12 through interconnection 16 and inputs electrically connected to the right 24a and left 24b mastoid pickups through interconnections 26a and 26b, respectively. The right 24a and left 24b mastoid pickups are conventional accelerometers or like vibration sensors similar to drill vibrational pickup 12. Adaptive controller 22, the output of which is connected to an input of equalizer 10 through interconnection 28, adaptively adjusts equalizer 10 using the vibration signals from drill vibration pickup 12, and right 24a and left 24b mastoid pickups. The adaptively equalized vibrations emanating from the right 18a and the left 18b head-worn vibrators are physically introduced into the patient 30 and cause vibrations in the inner ear. The vibration sensors and the vibrators are configured for coupling to the drill and the patient, using conventional coupling mechanisms.
However, the apparatuses disclosed in the ""426 and ""056 patents require a physical connection to the dentist""s drilling device to achieve an effective cancellation of intracranial noise. As such, a special drill with a proper connection must be provided for use, thereby precluding use of these apparatuses with conventional dental drilling-type equipment that is usually available in a dentist""s office. These apparatuses also employ a rather complex equalizing and adaptive controlling mechanism that is dependent upon a relatively remote input signal supplied from the drilling device for use in active cancellation of noise. Furthermore, due to direct coupling with the dentist""s drill, portability of these apparatuses is restricted. As a result, these apparatuses cannot be readily moved from one location to another for supporting a multitude of drilling operations, such as in a dental office arrangement supporting a variety of dental chairs in separate rooms or areas.
The apparatus for suppressing intracranial noise substantially departs from the prior art by providing a portable intracranial noise suppression apparatus for actively suppressing vibrational noise produced by a drilling medical instrument in a head of a patient.
The apparatus of the present invention uses an intracranial or vibrational noise signal that is available directly next to a patient""s ear as an input, thereby receiving a better estimate of the noise signal for active suppression than by receiving the input from a more remote location.
The apparatus provides an improved system for eliminating objectionable high-frequency sounds that a patient hears while undergoing dental work. In addition, the apparatus can be used when drilling or cutting of bone in a patient""s head or elsewhere could cause objectionable noise in the patient""s ears, such as during brain surgery. The system does not have to be physically connected to a dentist""s drilling equipment to perform its function.
The apparatus can be readily moved from one location to another for supporting a multitude of bone drilling or cutting operations, such as in a dental office arrangement supporting a variety of dental chairs in separate rooms or areas.
The apparatus includes a mechanism for sensing an intracranial vibrational signal induced within a patient""s head. The apparatus provides another mechanism for adaptively generating an intracranial vibrational suppression signal from the intracranial vibrational signal as a function of time. In addition, the apparatus includes yet another mechanism for applying the intracranial vibrational suppression signal to the patient""s head for suppressing the induced intracranial vibrational signal.